1. Field of the Invention
The present invention relates to a composition having non-Newtonian fluid behavior, and more particularly relates to a composition having thixotropic fluid behavior, which is suitable for use as a polishing solution.
2. Description of the Prior Art
With the progress of IC (integrated circuit) design and fabrication, chemical mechanical polishing (CMP) techniques have gradually become widely utilized in the process for manufacturing semiconductors having a line width of less than 0.35 .mu.m. In the chemical mechanical polishing process, the suspension of a polishing slurry is very critical to its application. That is, the suspension of the polishing slurry or its shelf life is dependent upon the dispersion of the particles in the polishing slurry. However, because of gravity, it is very difficult to suspend the abrasive material, such as aluminum oxide (Al.sub.2 O.sub.3), in the polishing slurry in a stable state.
U.S. Pat. No. 5,527,423 to Cabot Corporation discloses a polishing slurry of improved dispersion and suspension properties, which includes a surfactant. The incorporated surfactant can be a nonionic, anionic, cationic, or amphoteric surfactant. Representative examples of the surfactants include polyalkyl siloxanes, polyaryl siloxanes, and polyoxyalkylene ethers.
U.S. Pat. No. 5,693,239 and WO 97/13889 disclose a method for increasing the polishing efficiency of the polishing slurry by incorporating other different forms of particles into 1-50% of .alpha.-Al.sub.2 O.sub.3. The incorporated particles can be aluminum hydrates, aluminum hydroxide, .gamma.-alumina, .delta.-alumina, amorphous alumina, or amorphous silica. Neither surfactants nor soluble polymers are used.
U.S. Pat. No. 4,260,396 discloses a polishing composition for polishing silicon and germanium, which includes SiO.sub.2 and surfactants such as water soluble carboxypolymethylene gum and xanthum gum.
U.S. Pat. No. 4,475,981 discloses a method for polishing the Ni metal surface of a hard disc. The first step involves polishing the metal surface by a polishing slurry including Al.sub.2 O.sub.3 or CeO.sub.2 particles, Silconox Lap. as the dispersant, and hypochlorite as the oxidizing agent. The second step uses aluminum sol as a finer polishing agent to polish the metal surface.
In the above-mentioned conventional polishing slurries, the improvement to the suspension of particles in the liquid is achieved by incorporating surfactants or soluble polymers. However, the suspension of the particles is not satisfactory, foams will be generated in the process, and the incorporated surfactants or soluble polymers are actually deemed as contaminants in the high purity IC process. In addition, in some conventional slurries in which neither surfactants nor soluble polymers are incorporated, the suspension of the particles is also not satisfactory.